The present invention relates to the production of metals and alloys using the general method disclosed in U.S. Pat. Nos. 6,409,797; 5,958,106; and 5,779,761, all of which are incorporated herein, and preferably a method wherein titanium or an alloy thereof is made by the reduction of halides in a stream of reducing metal. Although the method disclosed herein is applicable to any of the hereinafter disclosed elements or alloys thereof, the invention will be described with respect to titanium and its alloys, simply because the available supply of titanium in the United States is now insufficient to meet the demand. Moreover, as the cost of titanium and its alloys is reduced by the use of the foregoing method, the demand will increase even beyond that already estimated by the aerospace companies and the Department of Defense.
Titanium is a very plentiful element distributed throughout the world, but it is very costly because of the antiquated methods by which it is produced. As is well known in the art, the Kroll and Hunter processes are the principal processes by which titanium is produced worldwide. Both of these processes are batch processes which produce in the first instance, a fused material of titanium and salt and excess reducing metal, magnesium for the Kroll process and sodium for the Hunter process. This fused material (known as sponge) then must be removed from the containers in which it was made, crushed and thereafter electrolytically purified in repeated steps.
The invention hereinafter described is a refinement of the Armstrong Process disclosed in the above incorporated U.S. patents.
Because titanium is an extremely reactive metal and is produced by the Armstrong Process as a very fine powder, generally with average diameters in the 0.1 to 1 micron range as calculated from BET surface area measurements, it is thereafter maintained at elevated temperature in order to increase the average particle diameter to greater than 1 micron. But, even at the large diameters, the powder is difficult to handle unless it has been passivated. By passivation, it is meant that a small amount of oxygen is introduced to the powder to form titanium dioxide on the surface so that the powder is not incendiary when exposed to air. Too much oxygen will increase the oxygen content beyond the ASTM specification for CP titanium grade 2 or for ASTM grade 5 titanium, that is 6/4 alloy (6% Al, 4% V by weight with the balance Ti). Heretofore, it was believed that the only practical way to passivate titanium powder was to bleed an inert gas such as argon with a very small percentage of oxygen for a time sufficient to increase the oxygen content on the surface of the powder to prevent spontaneous combustion when exposed to air. The times for passivation were measured in hours and was a design issue for large scale commercial plants based on a continuous process.
However, it has been unexpectedly and surprisingly found that passivation of titanium powder and/or titanium alloy powder can be accomplished by direct exposure to air and/or water and/or brine under certain conditions, which not only decrease the passivation time but also simplifies equipment design, thereby making the process simpler, more efficient and less expensive.